Prior art circuitry provided for circuits which would monitor the conditions of instruments such as valves and provide an indication of such conditions to an operator by way of control signals to the console graphics which were viewed by the operator. Thus the operator, by viewing the console graphics would know whether the valve was fully opened, fully closed or possibly in mid-travel between these two positions. Since the mid-travel indication of the valve could also be due to a failure in the valve condition sensing, mid-travel measurement was not reliable since it could be caused by either the valve actually being in mid-travel or a failure of the instrument sensors.
Thus there is a need for a reliable circuit that would not only provide the operator an indication of the instrument's condition, such as a valve being opened, closed, or in a mid-travel position, but also one which would provide the operator an indication that the actual sensing instrument was faulty.